Fructose metabolism in muscle differs litte from that of glucose. This dichotomy results from the different enzymes present in these various tissues.

Hexokinase, wich converts glucose to glucose-6-P on the entry into muscle cells, also phosphorylates fructose yielding fructose-6-P. The entry of fructose into glycolysis therefore involves only one reaction step, but also needs the hydrolysis of one ATP.

Fructose + ATP

Fructose-6-P + ADP

Liver contains little hexokinase; rather it contains glucokinase, wich phosphorylates only glucose. It converts frucotse to glycolytic intermediates through the pathway bellow:

Frutokinase catalyzes the phosphorylation of fructose by ATP at C1 to form fructose-1-P. Neither hexokinase nor phosphofructokinase can phosphorylate F1P at C6 to form glycolytic intermediate F16biP.

Claas I aldolase has several isoenzymic forms. Liver contais type B aldolase, wich besides F16biP also utilizes F1P as a substrate. F1P therefor undergoes an aldol cleavage.

Direct phosphorylation of glyceraldehyde by ATP through the action of glyceraldehyde kinase forms the glycolytic glyceraldehyde-3-P.